This invention relates generally to systems and methods of recharging batteries and, more particularly, to systems and methods of recharging batteries used to power motors. More particularly still, the invention provides a system and method that is particularly well suited for recharging the battery of a battery-powered, personal mobility cart having a motor and an "H-bridge" motor drive.
Electrical batteries are widely used to power a variety of electrical devices. Battery operation provides tremendous versatility, mobility and freedom by eliminating the need to connect a device with an external source of electrical energy. However, no battery can supply energy indefinitely. The need to recharge or replace spent batteries remains a cost of battery operation.
Advances in the battery art have improved the capacity, reliability and life of rechargeable batteries. Battery-powered devices using such batteries typically include a recharging circuit. When the battery-powered device is not in use, the recharging circuit takes energy from an external source, such as 120 VAC, 60 Hz. line currents and applies it to the battery to recharge it. This requires that the recharging circuit be connected with the external source and that the recharging circuit convert the external power to a form suitable for recharging the battery.
Advances in the battery art have made it practical to use rechargeable batteries in electric vehicles of various types. Common types of vehicles using battery-operated motor systems include small, short range, open vehicles such as golf carts, scooters for the elderly and disabled, and motorized wheelchairs. Other forms of battery-operated, motor-driven devices include cordless tools, appliances etc. In these devices, a large capacity battery supplies electrical power to a motor that, in turns drives the vehicle or device. Motor operation is controlled by a control circuit that can range in complexity and sophistication from a simple mechanical switch to a programmable, microprocessor-based system. Typically, a motor drive circuit under the command of the control circuit is provided for controlling the magnitude and direction of electrical current passing from the battery through the motor. One common form of motor drive is the "H-bridge" drive that includes four electronic switches that are arranged in an "H" configuration and are operable to direct variable width current pulses in either direction through the motor.
Electric vehicles typically perform considerable work and, thus, require considerable energy for battery recharging. In such vehicles, battery recharging is typically accomplished with a dedicated charging system powered by standard line current. Such battery chargers typically include a converter that rectifies and filters the AC source voltage and further include an inductor coupled to the converter through an electronic switch and to the battery through a diode. The electronic switch (typically a transistor) operates under the control of a control circuit to switch pulse-width modulated pulses of the rectified and filtered current to the inductor When the switch is "ON," energy is delivered to and stored in the field of the inductor. When the switch is "OFF," the energy stored in the coil is available for discharge from the coil. The diode is connected and polarized so that the battery is electrically isolated from the coil as the coil is charged and is electrically coupled to the coil as the coil discharges. Accordingly, energy introduced into the coil from the converter when the electronic switch is "ON" discharges into the battery when the electronic switch is "OFF." Such a charging system is known in the industry as a "buck" regulator.
The rate at which such a "buck" regulator can recharge a battery is largely dependent on the size of the inductor. Larger inductors can store more energy and, hence, deliver greater charging power to the battery than smaller inductors Larger inductors however, are physically larger, heavier and more expensive than smaller inductors Because inductors are typically the largest, heaviest and most expensive single component of a battery charging system, the desire for rapid charging is often tempered with the need to keep the size, weight and cost of the recharging system within reasonable limits.